Type:— MADAGASCAR. Antsiranana (Diego Suarez) Prov. Réserve spéciale de Manongarivo Ambahatra, cours supérieur; 13°59’S; 48°26’E. Crête entre les deux bras de l’Ambahatra, ca 800 m au N point côte au-dessus du camp 2, elevation: 1250–1300 m. Arête, dans une forêt montagnarde. Substrat: Rocher. (fragments of decaying wood can be observed on the lower side of the specimen). 9 March 1999, P. Geissler19691/1 (holotype: G!, isotypes: EGR!, GOET!).

Diagnosis:— In herbarium dark green plant with irregular branching, forming dense, adherent mat of 3–5 cm diameter. From the creeping, leafless but with scattered rhizoids covered, rhizomatous primary stem 5–10 mm long, often bifurcate branches arise. Leafy shoots 0.8–1.3 mm wide, sometimes flagelliform shoots also occur with reduced leaves (Fig. 1 A–B). Stem 80–130 μm thick, with 1(–2) layered cortex with pale rusty colored cell walls and 6–8 cells thick medulla of smaller cells with thinner, colorless walls (Fig. 1 C). Leaves, if intact, somewhat elongate, falcate with parallel and entire sides, convex, 400–500 μm long and 200–250 μm wide, apex rounded or 2–4 lobulate (Fig. 2). Insertion inverted J shaped, dorsal base cuneate, ventral base shortly decurrent to the midline of the stem, where very rarely filiform amphigastria occur (Fig. 1 D–E). The leaves are extremely fragile, many of them already at the habitat broken away along the midline of cell walls, forming an irregular dehiscence line (Fig. 3 A). The leaf fragments probably serve the purpose of vegetative propagation, although germinating fragments were not observed. Leaf cells 5- or 6-gonal, in the margin and at apex isodiametric, of 20–32 μm diameter, in the center and at leaf base somewhat elongate, 12–16 x 20–42 μm, walls with small, at the base with larger trigones (Figs. 3 B–D). Some oil bodies are persistent, ovate, exceeding the chloroplasts in size and seem to be slightly botryoidal. Autoicous. Androecia intercalar, consisting of 3–5 pairs of male bracts with acute ends sometimes pointed outwards. Gynoecia terminal or lateral supported by 1–2 bracts with acutely dentate margin. Perianth on a short, 80–120 μm long stalk, campanulate, almost terete with two very weak folds (Fig. 1 F). Perianth mouth fimbriate, with irregular, obtuse, 4–8 cells long fringes, 2–4 cells wide at their base (Fig. 3 E–F).

Etymology:— The specific epithet “ fracta ” has the meaning “broken” in Latin.

Recognition:— In North America and Asia several Plagiochila species with fragmenting leaves occur, but no other African species has such ones, which already in the field are irregularly broken into parts.Although the related and very widespread Plagiochila exigua (Taylor 1844: 179) Taylor (1846: 264) has caducous leaves, they are acutely bilobate, breaking away intact from their base. The doubtful Plagiochila artsii Pócs (2006: 334) has caducous, filamentous leaf lobes. In addition, the perianth mouth of Plagiochila fracta with obtuse fringes is also a good separating character distinguishing it from most African Plagiochila taxa.

Distribution:— The species is only known from the type. It seems to be endemic to the Manongarivo range in north-west Madagascar.

Remarks:— Several attempts were made in vain by French bryologists and by the author to again collect the above mentioned minuscule Plagiochila artsii on tree-fern stems at the type locality in Réunion Island. These repeated efforts suggest that the species described from small fragments, collected by the late Theo Arts, might be propagule shoots fallen off from the leaf surface of some other Plagiochila species.